Investments - Investments in Variable Interest Entities (Detail) - Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member] - USD ($)		Jun. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Investment	[1]	$ 106,492,000	$ 103,892,000
Maximum Exposure to Loss	[1]	$ 107,472,000	$ 104,872,000

[1] The Company has entered into a subordinated loan agreement with Aqua, whereby the Company agreed to lend the principal sum of $980.0 thousand. As of June 30, 2018 and December 31, 2017, the Company’s maximum exposure to loss with respect to its unconsolidated VIEs includes the sum of its equity investments in its unconsolidated VIEs and the $980.0 thousand subordinated loan to Aqua.